1. Field of Invention
This invention relates to a method and apparatus for determining an analyte and, in particular, to the determination of an analyte indicating a disease condition.
2. Background of the Invention
An accurate early and ongoing determination of a disease condition is important for the prevention and treatment of human and animal diseases. One class of diagnostic techniques uses immunoassay reactions to detect the presence of either an antigen or an antibody in a sample taken from a subject. These immunoassay methods include, for example, ELISA, immunochromatographic assays (strip tests, dipstick assays and lateral flow assays), and sandwich assays. Accuracy, reliability, and ease of use of these types of assays has improved, but often testing requires laboratory conditions, power supplies, and training that may not be available in some areas where testing is desired.
One type of sandwich assay uses gold-conjugated antibodies to enhance detection. For example, see PCT publication WO/91/01003. Enhancement of a gold colloid signal can be achieved by staining the gold colloids with silver. First, in the case of HIV, an HIV antigen is immobilized onto a solid polystyrene substrate. A human anti-HIV antibody is then captured by the antigen and is therefore itself immobilized on the substrate. The antibody is then exposed to anti-human IgG labeled with a colloidal gold particle and thus labeled IgG becomes bonded to the antibody. The antigen-antibody-IgG complex is then exposed to a solution containing silver ions and these become nucleated around the gold particles as solid silver particles having a dark color to the eye.
The development of microfluidics and microfluidic techniques has provided improved chemical and biological research tools, including platforms for performing chemical reactions, combining and separating fluids, diluting samples, and generating gradients. For example, see U.S. Pat. No. 6,645,432, hereby incorporated by reference herein.